Quartz is the second most common mineral (12%) found in the earth's crust. A wide variety of common gemstones, including Agate, Amethyst, Citrine, Jasper, Tiger Eye, and Onyx are all members of the quartz family. Ancient Greeks believed that rock crystal quartz was fossilized ice, and many scientists continued to believe this until the 16th century. Most quartz on todays market is lab grown, not to be confused with synthetic.